Ring roll replacing method in bar steel rolling mill and device therefor

ABSTRACT

The present invention relates to a method and apparatus for changing ring rolls of a bar and wire rod mill which makes roll changing work easy and in particular to a method for changing only the ring rolls without disassembling the housing in accordance with an optimum process. The method for changing ring rolls in a bar and wire rod mill having a plurality of roll assemblies incorporated into a housing and arranged in equiangular positions in circumferential direction comprises the steps of disengaging the interference fit between the spent ring rolls and the roll shaft, withdrawing the spent ring rolls by moving the roll shaft in an axial direction, changing the spent ring rolls with new ring rolls in the housing, inserting the roll shaft into the new ring rolls, and engaging the new ring rolls in interference fit with the roll shaft. Additionally, a main body of a bar and wire rod mill comprising a roll shaft suspending apparatus and a mechanism suitable for the method according to the present invention are provided.

TECHNICAL FIELD

[0001] The present invention relates to a method and apparatus forchanging ring rolls of a bar and wire rod mill which makes roll changingwork easy. Incidentally, the apparatus for changing ring rolls comprisesa main body of a bar roll mill having a roll changing mechanism and aroll shaft suspending apparatus.

BACKGROUND OF THE INVENTION

[0002] A plurality of sizing mills are arranged in the final stage of acontinuous rolling mill line for hot-rolling steel materials into barand/or wire rods. As the sizing mill, a bar and wire rod mill isprovided in which a plurality of roll assemblies supported by housingsare arranged in equiangular positions around the pass line. With regardto the roll assembly, it comprises a composite structure having ringrolls in contact with rolling materials and a roll shaft fitted into thebore of the ring rolls to support it.

[0003] Japanese Patent Laid-Open No. 104706/1999 discloses a bar andwire rod mill with a construction facilitating the changing operation ofthe ring rolls. This kind of roll mill has a plurality of roll units anda draft adjusting apparatus of an eccentric cartridge type for a rollunit mounted on the housing. Incidentally, the roll unit is synonymouswith the roll assembly. The housing consists of two pieces includingfirst and second housing parts capable of engaging with, and disengagingfrom, each other. A pair of journal bearing halves are formed in thecontact face of the first and second housing parts. The journal part ofeach roll unit held in an eccentric cartridge is sandwiched between theengaged journal bearing halves of the first and second housing parts.The roll changing operation of this bar and wire rod mill is performedas follows:

[0004] (1) Separate the second housing part from the first housing part;

[0005] (2) Take out the roll unit from the first housing part;

[0006] (3) Change the roll part of the disengaged roll unit;

[0007] (4) Incorporate the roll unit into the first housing part; and

[0008] (5) Engage the second housing part with the first housing part.

[0009] Hence, the roll changing operation is made easy because the rollmill can be disassembled and re-assembled through only a few steps.

[0010] However, the roll changing operation of such a bar and wire rodmill still has the following problems.

[0011] (1) In the case where the same roll shaft is used after the rollchanging operation, an operation to change the ring rolls separated fromthe roll shaft using an apparatus exclusively for this purpose isnecessary and the operation requires much time.

[0012] (2) In the case where a different roll shaft is used after theroll changing operation, it is necessary to stock a lot of roll shafts,which causes an increase in cost. Moreover, a large stock area is neededtoo.

[0013] (3) During the roll changing operation, the housing should bedisassembled into its two parts so that the journal bearing part or thelike is exposed. As a result, machine problems tend to be caused due tothe invasion of dust or moisture.

[0014] A method of roll changing which can resolve these problems, and amain body of a bar and wire rod mill and its peripheral apparatusadvantageous for performing such a method, are desired.

DISCLOSURE OF THE INVENTION

[0015] Hence, the inventors have developed a method for changing onlythe ring rolls without disassembling the housing, and found a rollchanging method comprising an optimum sequence of steps. In addition,the inventors have developed a main body of a bar and wire rod millcomprising a mechanism for changing only the ring rolls withoutdisassembling the housing, and a roll shaft suspending apparatus capableof dual-use for applying hydraulic oil pressure, required for engagingor disengaging the ring rolls and the roll shaft in interference fit,and for suspending the roll shaft, which is suitable for the rollchanging method of the invention.

[0016] In other words, the present invention relates to a method forchanging ring rolls used in a bar and wire rod mill having a pluralityof roll assemblies incorporated into a pair of housings and arranged inequiangular positions in circumferential direction, comprising the stepsof disengaging the interference fit between the spent ring rolls androll shaft, withdrawing the roll shaft from the spent ring rolls bylifting-up the roll shaft in an axial direction, changing the spent ringrolls for new ring rolls in said housings, inserting the roll shaft intothe new ring rolls, and engaging the new ring rolls with the roll shaftin interference fit.

[0017] According to the present method, only the ring rolls can bechanged without disassembling the housing.

[0018] Further, the present invention relates to a bar and wire rod millsuitable for applying the aforesaid method for changing ring rolls, inwhich a plurality of roll assemblies supported by a housing, comprisingring rolls capable of engaging with and disengaging from the roll shaftin interference fit and the roll shafts movable in an axial direction ina housing, are arranged in equiangular positions around the pass formedby these ring rolls.

[0019] According to one embodiment of the invention, the roll shaft canbe withdrawn from the ring rolls by means of a pushing or pulling actionof the roll shaft which is grasped at the end thereof Thus, after havingchanged the spent ring rolls for new ones, the roll shaft is insertedinto the new ring rolls and engaged therewith by interference fit.

[0020] Incidentally, it is preferable for the roll assembly to equipwith a mechanism for engaging or disengaging the ring rolls and the rollshaft in and from interference fit by the use of hydraulic oil pressure,a hydraulic oil passage being provided through the roll shaft from theend thereof and an oil inlet and a suspension jig receiving member bothbeing provided on one end portion of the roll shaft. Furthermore, it ispreferable for the internal surface of the ring roll and the journalpart of the roll shaft for the ring roll of the roll assemblies to formtapered surfaces.

[0021] The roll shaft can be engaged with, or disengaged from, the ringrolls in interference fit by applying hydraulic oil pressure through theoil passage inside the roll shaft from the end thereof to make bothtapered surfaces either engaged in tight contact fit or disengaged fromeach other. Furthermore, as the journal part of the roll shaft for thering rolls and the ring rolls are engaged or disengaged through thetapered surface, the interference fit can be made firm to a greaterextent and the disengagement can be made smooth to a greater degree dueto the wedge effect of the tapered surface.

[0022] In addition, as the end part of the roll shaft for applyinghydraulic pressure is arranged outside the housing, both taperedsurfaces can be engaged or disengaged freely by applying hydraulic oilpressure from outside the housing successively to all of the rollassembly.

[0023] Incidentally, all of the multiple roll assembly can be of themotor driven type or some of them may be motor driven while others arenot.

[0024] In view of a use, the bar and wire rod mill according to thepresent invention may preferably be a four-roll mill comprising fourpieces of roll assembly, supported by a housing arranged in equiangularpositions around a pass.

[0025] Moreover, embodiments of the present invention relate to a rollshaft suspending apparatus suitable for use in the method for changingring rolls as disclosed, comprising a nozzle for injecting hydraulic oilinto the oil inlet provided on one end of the roll shaft, a rod holdingthe nozzle at the top end thereof and an internal oil feed passageconnected to the nozzle through the rod, a cylinder embracing the rodfor reciprocal actuation by means of hydraulic oil pressure, and a frontend of a rod suspending apparatus engaged with the suspension jigreceiving member provided on one end of the roll shaft. It may befurther preferable to provide a mechanism by which the rod holds thenozzle through a resilient seat.

[0026] A more steady and quick change of the roll is made possible byapplying the roll shaft suspending apparatus in accordance with themethod of the invention. It is performed according to the followingoperation in which the roll shaft of the roll assembly with the roll tobe changed is set in an upright position before disengaging the spentring rolls from the interference fit with the roll shaft, and then thesuspending apparatus and one end portion of the roll shaft are coupledtogether before withdrawing the roll shaft from the spent ring rolls soas to connect the hydraulic piping inside the roll shaft with thehydraulic oil pressure source via the one end portion of the roll shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a cross-sectional view showing the main part of thestructure of the bar and wire rod mill according to an embodiment of thepresent invention;

[0028]FIG. 2 is a cross-sectional view showing a means for applyinghydraulic oil pressure to the tapered surfaces;

[0029]FIGS. 3a to 3 j are drawings illustrating a process involvingsteps a to j for changing ring rolls employed in a bar and wire rod millaccording to the present invention;

[0030]FIGS. 4a to 4 e are drawings illustrating a process involvingsteps a to e for changing ring rolls using a roll shaft suspendingapparatus according to the present invention; and

[0031]FIG. 5 is a cross-sectional view showing the top end portion of arod together with a pawl plate fitted in the groove.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032] The present invention shall now be described in more detail withan example of a bar and wire rod mill (referred to as a four-roll millhereafter) having four roll assemblies arranged in equiangular positionsaround the pass and supported by the housing.

[0033]FIG. 1 is a cross-sectional view showing the main part of thestructure of the four-roll mill according to the present invention. InFIG. 1 a quarter portion centered around the pass 16 is illustrated. Thewhole view can be obtained from the combination of each rotated view ofFIG. 1 by 90°, 180° and 270°.

[0034] The roll assembly is constructed by attaching a ring roll 2 tothe journal part 1A located in the lower side of a roll shaft 1. Theouter circumferential surface of the ring roll 2 is configured as theworking surface of the roll. Both of the outer circumferential surfaceof the journal part 1A, which is an engagement part of the roll shaft 1and the ring roll 2, and the internal surface of the ring roll 2 have atapered surface, and both tapered parts are engaged together ininterference fit. Incidentally, in this example, the outercircumferential surface of the journal part 1A is a tapered male surfacehaving upward inclination toward the upper end of the roll shaft 1. Ataper sleeve 3, having its internal surface tapered so as to slidablymate with the tapered male surface of the said journal part 1A, isfitted into the internal surface of the ring roll 2. The engagement orthe disengagement of the roll shaft 1 and the ring roll 2 ininterference fit is performed by engaging or disengaging the male andfemale tapered surfaces by means of, for example, applied hydraulic oilpressure.

[0035] Bearings 4A and 4B are mounted on respective positions oppositeto each other across the ring journal part 1A of the lower portion ofthe roll shaft 1, and a bearing 5 is mounted on a position of the upperportion thereof. The lower portion bearings 4A and 4B are supported by ahousing 8 through a lower eccentric cartridge 6A. The upper portionbearing 5 is supported by a housing 8 through an upper eccentriccartridge 6B and a thrust adjusting screw 7. Incidentally, the upper endportion of the roll shaft is exposed outside the housing 8.

[0036] The lower eccentric cartridge 6A supports the bearing 4A, 4B andthe upper eccentric cartridge 6B supports the bearing 5 slidably alongthe axial direction of the roll, respectively. The lower eccentriccartridge 6A and the upper eccentric cartridge 6B, that can rotatearound their own shaft, are supported by the housing 8. By rotating thelower eccentric cartridge 6A around its own shaft, the center of theroll shaft 1 rotates around the center of the lower eccentric cartridge6A. The upper eccentric cartridge is also rotated likewise. As describedabove, the eccentric cartridge 6 moves the roll shaft 1 along thedirection perpendicular thereto so that it is used for the adjustment ofthe distance from the center of the ring roll 2 to the center of thepass, namely the rolling position. Incidentally, the lower eccentriccartridge 6A and the upper eccentric cartridge 6B are interconnected toeach other and the distance between them can be varied. In addition, thebearing 5 is held by a fastening screw 9 to the upper eccentriccartridge 6B.

[0037] In such a structure as described above, the external diameter ofthe bearing 4A and 4B is set to be less than the internal diameter ofthe tapered sleeve 3 so as to disengage the tapered surface of the rollshaft 1 and the ring roll 2 from each other. Further, the fasteningscrew 9 is disengaged to move the roll shaft 1 along the axial directionthereof. As a result, the roll shaft 1 can be withdrawn from the ringroll 2.

[0038] The thrust adjusting screw 7 supports the upper eccentriccartridge 6B with its inner peripheral surface so as to rotate aroundits own shaft. In addition, the thrust adjusting screw 7 is engaged bymeans of a thread on its periphery with the screw receiving member 10which is held by a screw to the housing 8. Further, the thrust adjustingscrew 7 is connected to the screw receiving member 10 by means of aclamp bolt 11. Therefore, by loosening the clamp bolt 11 and driving thethrust adjusting screw 7, the position of the roll assembly along theaxial direction of the roll can be adjusted.

[0039]FIG. 2 is a cross-sectional view showing a means for applyinghydraulic oil pressure to the tapered surfaces. An oil feed passage 12extends through the inside of the roll shaft from an oil inlet 12A inthe end face of the roll shaft to an oil outlet 12B. The end portion ofthe roll shaft where the oil inlet 12A opens is extended outside of thehousing, and a circumferential groove 22 is provided on the extended endportion of the roll shaft. The circumferential groove 22 serves as areceiving part for the suspension jig when suspending the roll shaft 1.Additionally, the oil outlet 12B opens at a plurality of positions overthe tapered surface of the journal part 1A of the ring.

[0040] In the case where the tapered surfaces are in interference fitwith each other in the initial state, the injection of high pressure oilfrom the oil inlet 12A makes the internal diameter of the tapered sleeve3 expand within its elastic limit by means of the hydraulic oil pressurefrom the oil inlet 12A. In addition, due to the expansion of the insidediameter, a counter force is generated between the two tapered surfacesto facilitate their disengagement from each other. Afterwards thehydraulic oil pressure is decreased and when the inside diameter isrestored to its original size, both tapered surfaces are left in adisengaged condition. Consequently, the roll shaft 1 can be withdrawnout of the ring roll 2 by pulling it toward the outside of the housing.

[0041] On the other hand, in the case where the tapered surfaces are ina disengaged condition from each other in the initial state, byinjecting high pressurized oil while pushing the roll shaft 1 toward theinside of the housing with enough force to overcome the counter forcegenerated between both tapered surfaces, the roll shaft 1 enters intothe smaller diameter part of the tapered sleeve 3 which has its internaldiameter expanded by means of the hydraulic oil pressure. Afterwards,the hydraulic oil pressure is decreased and when the internal diameteris restored to its original size, a firm, tight contact between bothtapered surfaces can be obtained.

[0042] As described above, according to the bar and wire rod mill of theinvention, the interference fit and its release between the ring rollsand the roll shaft can be performed within the housing. In other words,only the ring rolls can be changed without disassembling the housing.

[0043] A process of changing a roll of a four-roll mill shall now beexplained. This process is performed according to the steps describedbelow and is illustrated in FIGS. 3a to 3 j.

[0044] (I) Preparation of the Housing

[0045] (1) Set the housing on a change table using a crane or the like;

[0046] (2) Disengage the roll mill guide (including an installing jigfor on line); and

[0047] (3) Align the eccentric position of the eccentric cartridge to apredetermined position.

[0048] (II) Change of Roll

[0049] (Disengaging Operation)

[0050] (1) Operate the change table to rotate the housing and set theroll shaft in an upright position. Incidentally, the exposed end of theroll shaft is set in the upper position;

[0051] (2) Loosen the clamp bolt 11 (FIG. 3a);

[0052] (3) Drive the thrust adjusting screw 7 to lower down the rollassembly so as to make the lower end of the ring roll 2 come in contactwith the lower eccentric cartridge 6A (FIG. 3a);

[0053] (4) Unscrew the fastening screw 9 (FIG. 3b);

[0054] (5) Mount the push ring 13 on the roll shaft 1 (FIG. 3b);

[0055] (6) Set the oil injection apparatus 14 at its operating position(FIG. 3c);

[0056] (7) Couple the injection nozzle 14B with the oil inlet providedon the end portion of the roll shaft (FIG. 3d);

[0057] (8) Push the push ring 13 by means of a shock absorbing cylinder14A (FIG. 3d);

[0058] (9) Increase the oil pressure in the injection nozzle 14B anddecrease the oil pressure in the shock absorbing cylinder 14A (FIG. 3e).The tapered surfaces are now separated;

[0059] (10) Lift up the shock absorbing cylinder 14A and release thepushing force on the push ring (FIG. 3f);

[0060] (11) Remove the injection nozzle 14B from the oil inlet providedon the end portion of the roll shaft (FIG. 3f);

[0061] (12) Return the oil injection apparatus 14 to a waiting position;

[0062] (13) Remove the push ring 13 from the roll shaft 1 (FIG. 3g);

[0063] (14) Set the lifting apparatus 15 at its operating position (FIG.3g);

[0064] (15) Lower the hook 15B by means of the lifting cylinder 15A(FIG. 3h);

[0065] (16) Fix the hook 15B onto the roll shaft 1 (FIG. 3h);

[0066] (17) Lift up the roll shaft 1 using the hook 15B and the liftingcylinder 15A and withdraw it from the ring roll 2 (FIG. 3i); and

[0067] (18) Take the ring roll 2 out of the housing (FIG. 3j).

[0068] (Assembling Operation)

[0069] (19) Insert a new ring roll 2 into the housing;

[0070] (20) Lower the roll shaft 1 into the ring rolls using the hook15B and the lifting cylinder 15A;

[0071] (21) Remove the hook 15B from the roll shaft 1;

[0072] (22) Lift up the hook by means of the lifting cylinder 15A;

[0073] (23) Return the lifting apparatus to the standby position;

[0074] (24) Mount the push ring on the roll shaft;

[0075] (25) Set the oil injection apparatus at its operating position;

[0076] (26) Couple the injection nozzle with the oil inlet provided onthe end portion of the roll shaft;

[0077] (27) Increase the oil pressure inside the injection nozzle whilepushing the push ring by means of the shock absorbing cylinder. Thetapered surfaces are now in close contact;

[0078] (28) Lift up the shock absorbing cylinder and release the pushingforce from the push ring;

[0079] (29) Remove the injection nozzle from the end portion of the rollshaft;

[0080] (30) Return the oil injection apparatus to the standby position;

[0081] (31) Remove the push ring from the roll shaft;

[0082] (32) Fix the fastening screw; and

[0083] (33) Coarsely adjust the position of the roll assembly along theaxial direction of the roll by driving the thrust adjusting screw andtighten the clamp bolt.

[0084] (III) Successively rotate the housing on the change table by 90°and repeat the above operation (II).

[0085] (IV) Final Roll Position Adjusting Operation

[0086] (1) Put the housing in a condition suitable for mounting aprojector, which is an apparatus for projecting the externalcircumferential profile of the ring rolls on to a monitor screen;

[0087] (2) Set the projector;

[0088] (3) Loosen the clamp bolt and align the roll center by means of athrust adjusting screw;

[0089] (4) Tighten the clamp bolt and fix the thrust adjusting screw;

[0090] (5) Rotate the eccentric cartridge and set the roll gap;

[0091] (6) Remove the projector; and

[0092] (7) Remove the housing from the change table.

[0093] An example of the roll shaft suspending apparatus according tothe present invention shall now be described with reference to FIG. 4a.The upper half of FIG. 4a shows a roll shaft suspending apparatusaccording to the present invention and the lower half shows a part ofthe bar and wire rod mill. The roll shaft suspending apparatus comprisesa nozzle 115 for injecting hydraulic oil into the oil inlet 131 providedon the upper end of the roll shaft 101 of the bar and wire rod mill, arod 116 holding on the top end thereof the nozzle 115 and having an oilfeed passage 117 inside thereof connecting with the nozzle 115, and acylinder 118 embracing the rod 116 for actuating it reciprocally bymeans of hydraulic oil pressure.

[0094] The high pressurized oil is injected from the oil inlet 126 ofthe oil feed passage 117. The maximum injection pressure of the highpressurized oil is about 2000 kgf/cm² and it is preferred to set acertain pressure to cause the deformation of the tapered surface withinits elastic limit. Upon the injection of the hydraulic oil, the rod 116pushes down the roll shaft 101. In addition, after the release of theinterference fit between the ring roll 102 and the roll shaft 101, therod 116 lifts up the roll shaft 101. For such pushing down and liftingit is preferable to set the operating pressure of the rod 116 of thehydraulic oil cylinder 118 to a maximum of about 700 kgf/cm² (69 MPa) inorder to enable a smooth motion of the roll shaft.

[0095] The nozzle 115 on the top end portion of the rod 116 may be fixedin place by a screw or the like. However, as described in this example,it is preferable to hold the nozzle in place with a resilient seat 125,such as a compression spring or a hydraulic cylinder, because the shockgenerated upon the injection of the high pressurized oil can beminimised more effectively.

[0096] Incidentally, when it is difficult to push on the end of the rollshaft directly by the top of the rod, it is better to use a pushing jigfor transmitting the pushing force. The push ring 119 shown in FIG. 4bis an example of such use. In this case, it is preferable to provide onthe top end of the rod 116 a pushing jig receiving member which engageswith the pushing jig. Ring fitting hole 121 corresponds to the pushingjig receiving member.

[0097] The roll shaft suspending apparatus according to the presentinvention further comprises essentially a suspension jig engaging withthe suspension jig receiving member provided on the end portion of theroll shaft. A circumferential groove 122 which acts as the suspensionjig receiving member and a groove fitting pawl plate 123 which acts asthe suspension jig to be engaging with the receiving member areillustrated in FIG. 4a. The use of this suspension jig on the lower endof the rod (116) makes it possible to lift up the roll shaft 101, havingbeen disengaged from the interference fit with the ring roll 102, bymeans of the upward pulling force of the hydraulic cylinder 118.

[0098] The groove fitting pawl plate 123 is, for example, preferably anarc shaped half as shown in FIG. 5. In addition, in terms of operationefficiency and safety, the roll shaft suspending apparatus according tothe present invention is preferably fixed to a mount base 127 as shownin FIG. 4a, having a rigid and firm construction of steel frames or thelike.

[0099] The process of changing the ring rolls of the bar and wire rodmill using the roll shaft suspending apparatus according to the presentinvention is explained hereinafter with reference to FIGS. 4a to 4 e.The description is omitted about the operation performed before andafter the process in which the roll shaft suspending apparatus is out ofuse.

[0100] (I) Rotate the change table (rotatable, but not shown) with thehousing 111 thereon and move the roll assembly 120 to the position justbelow the nozzle 115. After having aligned the center line of the nozzle115 with the center line of the oil inlet 131, release the fasteningbolt 112. Then drive the screw 107 to lower the roll assembly 120 untilit contacts with the eccentric cartridge 106 of the ring roll 102 (FIG.4a);

[0101] (II) Loosen the clamp bolt 110 to disengage the screw holder 109from the housing 111. Afterwards, set the push ring 119 (FIG. 4b);

[0102] (III) Select the “push mode” of the cylinder 118 to advance therod 116 until it contacts with the push ring 119. Hence, the nozzle 115is connected automatically to the oil inlet 131. Then, fit the groovefitting pawl plate 123 into the circumferential groove 122 (FIG. 4c);

[0103] (IV) Inject high pressurized oil from the oil inlet 126. Thejournal part of the ring 101A and the tapered surface of the tapersleeve 102A deform within their elastic limits and are therebydisengaged from the interference fit. The roll shaft is lifted a littleapart from the ring roll 102 (FIG. 4d);

[0104] (V) Select the “pull mode” of the cylinder 118 to pull back therod 116. Hence, the roll shaft 101 is withdrawn upwardly from the ringroll 102 (FIG. 4e); and

[0105] (VI) Take the ring roll 102 out of the housing 111 and insert anew ring roll. Afterwards, perform the process (I) to (V) inversely.Incidentally, the operation can also be performed inversely by, forexample, “pulling” instead of “pushing”.

[0106] Finally, perform the above described operations (I) to (VI) foreach of the plurality of rolls within the housing.

[0107] Industrial Applicability

[0108] According to the present invention various kinds of superioreffects are obtained as described below.

[0109] The disassembling process of the housing can be dispensed with sothat the time needed for changing the roll is reduced and the labor costcan be cut down.

[0110] Machine problems are reduced because the disassembly of thehousing is not involved so that the working ratio and the productivityof the facilities are improved.

[0111] As the changing operation of the roll shaft is not required, thenumber of equipment stocksare reduced so that the storage space can becut down.

[0112] The conventional method for changing the roll involves thedisassembly of the housing and therefore needs a housing disassemblingapparatus and a roll changing apparatus, whereas the present inventiononly requires the roll changing apparatus and therefore the number ofequipment stocks are reduced.

[0113] The handling subject was conventionally a roll assembly, but thepresent invention involves ring rolls, thereby making the subject lightweight so that the safety aspect is improved.

[0114] Furthermore, with the use of the roll suspending apparatusaccording to the present invention, the changing operation of the ringrolls can be performed within a single apparatus. Therefore, theoperability and the work efficiency are improved and the working spacecan be reduced.

[0115] Additionally, as the tapered surfaces of the inside of the ringrolls and the journal part of the roll shaft for the ring rolls areunder the pressure of the injected hydraulic oil, the pressure insliding at the engagement surface is low and the surface is welllubricated. Therefore, the tapered surface is free from abrasion ordeformation and the machine can be maintained in a sound condition for along time. As a result, the lifetimes of the components are extended andthe problem caused by insufficient torque rarely happens.

1. A method for changing ring rolls in a bar and wire rod mill having aplurality of roll assemblies incorporated into a housing and arranged inequiangular positions in circumferential direction, characterized bycomprising the steps of: disengaging a spent ring roll and its rollshaft from interference fit; withdrawing the spent ring roll by movingthe roll shaft in the axial direction; changing the spent ring roll fora new ring roll in the housing; inserting the roll shaft into the newring roll; and engaging the new ring roll and the roll shaft ininterference fit each other.
 2. The method according to claim 1, whereinhydraulic oil pressure is used for engaging and disengaging the ringroll and the roll shaft in and from interference fit.
 3. The methodaccording to claim 2, further comprising the steps of: holding the rollshaft of the roll assembly, in which the spent roll is to be changed, inan upright position before disengaging the spent ring roll and the rollshaft from the interference fit; and coupling a suspending apparatuswith one end of the roll shaft and connecting a hydraulic oil passagewithin the roll shaft to a hydraulic oil source through said end of theroll shaft before withdrawing the roll shaft from the spent ring roll.4. A bar and wire rod mill comprising a plurality of roll assemblieseach having a ring roll capable of engaging and disengaging a roll shaftin and from interference fit, wherein the roll shaft is movable in theaxial direction within a housing said plurality of roll assemblies beingarranged in equiangular positions around a pass and supported by saidhousing.
 5. The bar and wire rod mill according to claim 4, wherein eachroll assembly comprises: a mechanism for engaging or disengaging thering roll and the roll shaft in and from interference fit by means ofhydraulic oil, with the inner surface of the ring roll and the journalpart of the roll shaft having a tapered surface; hydraulic oil passageextending through the roll shaft from one end portion of the roll shaft;and a hydraulic oil inlet and a suspension jig receiving member providedon one end of the roll shaft.
 6. The bar and wire rod mill according toclaim 5 wherein there are four roll assemblies.
 7. A roll shaftsuspending apparatus comprising: a nozzle for injecting hydraulic oilinto an oil inlet provided on one end portion of a roll shaft of a rollassembly; a rod holding said nozzle on the top end portion thereof andhaving a hydraulic oil passage therethrough connecting with said nozzle;a cylinder embracing said rod for actuating it reciprocally by hydraulicoil pressure; and a suspension jig for engaging with a suspension jigreceiving member provided on one end of said roll shaft.
 8. The rollshaft suspending apparatus according to claim 8, wherein said rod holdssaid nozzle through a resilient seat.